Q&As About Implementing the 2010 Guidelines for Obstetric Providers
Q: I have a patient who had a urine culture positive for GBS early in pregnancy. Do I still need to screen her at 35-37 weeks gestation?
A: No. The guidelines (Table 3) indicate that a woman who has GBS bacteriuria at any time during the current pregnancy will require intrapartum antibiotic prophylaxis regardless of subsequent testing, so screening a woman with GBS bacteriuria during the current pregnancy is not necessary.
Q: With the new guidelines, should I consider a woman GBS positive if her urine culture reports that she has <10,000 cfu/mL?
A: Yes. If a urine culture is reported as positive for GBS, that woman should be considered GBS positive. While guidelines now require that labs only report relatively high (i.e., 104 colony forming units/mL) colony counts of GBS in urine cultures, we recommend that providers manage all GBS positive urine cultures equally, regardless of colony count, and consider any woman with a urine culture positive for GBS to be GBS positive for that pregnancy.
Q: I have a patient who had a urine culture that was positive for GBS early in pregnancy; she was treated, and repeat urine cultures were negative. Does she still require intrapartum antibiotic prophylaxis?
A: Yes. Studies have shown that GBS bacteriuria is a sign of heavy GBS colonization, which may not be entirely eradicated with treatment. GBS bacteriuria is a risk factor for having an infant with early-onset GBS disease. This patient should thus receive intrapartum antibiotic prophylaxis, and does not require screening for GBS at 35-37 weeks because regardless of that screening result she will require intrapartum antibiotic prophylaxis.
Q: When is the best time to screen for GBS in pregnancy?
A: Studies have shown that testing within 5 weeks of delivery is most accurate at predicting GBS status at delivery, with a negative predictive value of 95-98% and a positive predictive value of 87-100% if performed in that time period. Positive predictive value decreases significantly to 43% if done 6 weeks or more prior to delivery. Because the performance of screening is best if done within 5 weeks of delivery, and most women deliver at term, the guidelines state that screening for GBS should be done between 35-37 weeks gestation.
Q: I have a patient who was admitted in preterm labor at 29 weeks and screened negative for GBS at that time, and then didn't deliver. She is now 36 weeks and is being seen in the office for routine prenatal care. Do I need to re-screen her?
A: Yes. Although this woman was screened earlier in gestation because of preterm labor, she may have acquired GBS colonization since that time, and should be screened again at 35-37 weeks if she has not delivered.
Q: I have a patient who was admitted in preterm labor at 29 weeks and screened positive for GBS at that time, and then didn't deliver. She is now 36 weeks and is being seen in the office for routine prenatal care. Do I need to re-screen her?
A: No. Women who are screened earlier in gestation because of threatened preterm delivery and are GBS positive but don't deliver at that time should receive prophylaxis when they go into true labor. They do not need to be rescreened during the pregnancy.
Q: Do I still need to screen a woman for whom I am planning a cesarean delivery?
A: Yes, because GBS positive women will still need prophylaxis if cesarean delivery is performed after onset of labor or after rupture of membranes (Table 3). Since it is not possible to predict if a woman will labor or rupture membranes prior to cesarean delivery, women for whom a cesarean section is planned should still be screened for GBS.
Q: If a culture is done at 35 weeks gestation and it is negative, and the patient comes in at 41 weeks gestation (more than 5 weeks later), does another culture need to be done?
A: No. All women should be screened between 35-37 weeks; if this result is negative, then no further testing needs to be done. However, if a woman is cultured before 35 weeks, she should be rescreened if presenting for labor 5 or more weeks later.
Q: To screen for GBS, do I have to do a vaginal swab, a rectal swab, or both?
A: Current guidelines require a vaginal-rectal swab, because the sensitivity of vaginal-rectal swab is higher than vaginal swabs alone for detection of GBS. There are not enough data to know whether perianal or vaginal-perianal swabs are adequately sensitive. To obtain an adequate sample, a provider should swab inside of the lower vagina (introitus) and then insert the swab through the anal sphincter. The same swab can be used, or 2 different swabs can be used, if desired.
Q: If a woman with unknown GBS status is admitted with pPROM (preterm premature rupture of membranes) and I think she will deliver within the next 24 hours, do I still need to screen for GBS?
A: Yes, screening is required (Figure 6). This is important because many women who present with pPROM do not deliver imminently. The GBS culture results will guide whether or not these women need intrapartum antibiotic prophylaxis.
Q: Is there any 'rapid screening' for GBS that is acceptable for women who present in labor with unknown colonization status and no other indications for intrapartum prophylaxis?
A:Yes, rapid intrapartum nucleic acid amplification tests (NAAT) such as PCR can be performed, where available, on women with unknown GBS colonization and no other indications for intrapartum prophylaxis (delivery at <37 weeks, GBS bacteriuria during the current pregnancy, previous infant with GBS disease, rupture of membranes of ≥ 18 hours, temperature of ≥100.4° F). As with culture, it is still important to collect a vaginal-rectal sample for these tests. Women who test positive should get intrapartum prophylaxis. In contrast to culture, women who test negative should also be given intrapartum prophylaxis if they develop one of the indications for intrapartum prophylaxis (rupture of membranes of ≥ 18 hours, temperature of ≥100.4° F) at any point during labor (Table 3). This is because some studies have shown that the sensitivity of PCR performed directly on vaginal/rectal swabs without an enrichment step was less than that of culture. Thus, clinicians should remember that in this unique circumstance intrapartum risk factors trump negative test results.
Q: If a woman's rapid intrapartum test is negative, and she develops a fever >100.4°F during labor, does she need intrapartum antibiotic prophylaxis?
A: Yes. A negative rapid intrapartum test is not as reliable as a positive result due to the lower sensitivity of the technique compared with enriched culture. Thus, women who develop a temperature of ≥100.4° who have ruptured membranes for ≥18 hours should still receive intrapartum antibiotic prophylaxis, although their rapid intrapartum test is negative (Table 3).
Q: Does a cesarean section reduce all risk of an infant acquiring early-onset GBS disease?
A: No. Studies have shown GBS can be transmitted from mother to infant even through intact membranes and even in the absence of labor. However, the risk for transmission is quite small until labor begins or membranes rupture, which is why GBS positive women who have labored or who have ruptured membranes require antibiotic prophylaxis even if they are undergoing cesarean section.
Q: At what point should I start antibiotics for a GBS positive woman who presents in labor?
A: GBS positive women in labor should receive antibiotics as soon as possible after presentation in labor. The guidelines recommend that intrapartum antibiotic prophylaxis be initiated ≥4 hours prior to delivery for optimal prophylaxis, and continue as long as active, progressive labor continues. Thus, it is important that intrapartum antibiotic prophylaxis be initiated as soon as possible after presentation in labor to ensure adequate prevention.
Q: Does the CDC have any recommendations on the use of internal fetal monitoring (scalp electrodes) for women receiving GBS intrapartum antibiotic prophylaxis?
A: Although concern has been raised about performing certain obstetric procedures such as internal fetal monitoring, and also membrane stripping and mechanical and/or pharmacologic cervical ripening on GBS-colonized women, available data are not sufficient to determine whether these procedures are associated with an increased risk for early-onset GBS disease. Clinical judgment should dictate the use of these procedures, and intrapartum antibiotic prophylaxis should continue as recommended.
Q: Should I delay amniotomy in a GBS+ woman until she has received adequate prophylaxis?
A: Although concern has been raised that artificial membrane rupture could facilitate transmission of GBS from mother to infant, available data are not sufficient to demonstrate risk or to guide the timing of amniotomy or other procedures intended to facilitate progression of labor in GBS-colonized women. Intrapartum antibiotic prophylaxis is optimal if ≥4 hours in duration, and if possible, amniotomy should be timed accordingly. However, no medically urgent procedure should be delayed in order to achieve a certain duration of intrapartum antibiotic prophylaxis.
Q: If a GBS-colonized woman who was going to have a planned cesarean delivery is admitted in active labor and is given penicillin prophylaxis, should we then delay her cesarean for four hours if possible?
A: It is important that any GBS positive woman should receive intrapartum prophylaxis as soon as possible after presenting in labor, even if the mode of delivery is cesarean section. However, no medically urgent procedure should be delayed in order to achieve a certain duration of intrapartum antibiotic prophylaxis.
Antibiotic Issues & Options
Q: Is the regimen I use for latency in a woman presenting with preterm premature rupture of membranes (pPROM) adequate for GBS prophylaxis?
A: If the regimen for latency includes ampicillin (given 2 g IV x 1, then 1 g IV every 6 hours for at least 48 hours) then it is adequate prophylaxis for GBS. Other regimens are not adequate for GBS prevention.
Q: My penicillin-allergic patient is at high risk for anaphylaxis, and I requested resistance testing be done on her culture. Her GBS culture was reported as 'resistant to erythromycin, and D zone positive.' What does this mean?
A: When bacteria are resistant to erythromycin they can have inducible resistance to clindamycin; ordinary susceptibility testing won’t detect this. A separate test must be done for inducible resistance, in addition to susceptibility testing. D-zone testing is one way of testing for inducible resistance; a positive result means that inducible resistance is present. In this example, the result signifies that the bacteria is resistant to erythromycin and has inducible resistance to clindamycin. This means that clindamycin is not an appropriate choice for intrapartum antibiotic prophylaxis for this patient. This patient, because she is at high risk for anaphylaxis to penicillin, should receive vancomycin.
Q: How do I choose between 2.5 and 3 million units of penicillin for subsequent doses of penicillin?
A: As a provider, you can choose to give any amount of penicillin between 2.5 and 3 million units that is convenient for your clinical setting (Figure 8, 2nd footnote). This range of values was provided as hospital pharmacies may have different formulations of penicillin readily available. All doses within this range are expected to provide the same degree of protection.
Q: If a GBS positive patient has a history of penicillin allergy but is not high risk for anaphylaxis (i.e., has no history of anaphylaxis, angioedema, respiratory distress or urticaria after receiving penicillin or a cephalosporin), what antibiotic should she receive?
A: Cefazolin is the drug of choice in this circumstance (Figure 8). Unfortunately, many providers prefer to use clindamycin because they are concerned about anaphylaxis to cefazolin. These clinicians may not realize that cefazolin has similar pharmacokinetics to penicillin and concentrates very well in amniotic tissues, so it is strongly preferred over clindamycin which has limited ability to concentrate in fetal tissues and amniotic fluid. Additionally, only approximately 10% of patients with penicillin allergy have immediate hypersensitivity reactions to cephalosporins; only 4 reports of nonfatal cases of anaphylaxis associated with GBS chemoprophylaxis have been published since 1996 when GBS guidelines for chemoprophylaxis were first released. Thus, while it may seem safer to choose clindamycin, the use of clindamycin over cefazolin may actually elevate the risk that intrapartum prophylaxis fails.
Q: Why is it important to assess for risk for anaphylaxis in GBS positive women who are penicillin-allergic?
A: Assessing this risk will help you choose the most effective drug for intrapartum prophylaxis in your penicillin allergic patients. Unless a woman is at high risk for anaphylaxis (i.e., had angioedema, a history of anapylaxis, respiratory distress, or urticaria following penicillin administration), cefazolin can and should be used (Figure 8). Cefazolin has similar pharmacokinetics to penicillin and concentrates very well in amniotic tissues, so it is strongly preferred over clindamycin which has limited ability to concentrate in fetal tissues and amniotic fluid.
Q: I have a GBS positive patient who is allergic to penicillin, and has a history of urticaria and angioedema after receiving penicillin. I requested susceptibility testing but do not have the results. What antibiotic should she receive?
A: Given that susceptibility testing results are not available, this patient should receive vancomycin for intrapartum antibiotic prophylaxis (Figure 8). It is preferable, however, to have susceptibility testing results available if at all possible as vancomycin is thought to be less effective than clindamycin with respect to intrapartum antibiotic prophylaxis for GBS. Vancomycin is also an agent to use judiciously since it is a drug of last resort for many bacterial infections.
Q: My patient is GBS positive and has a history of anaphylaxis to penicillin. Based on CDC guidelines, I requested susceptibility testing when I sent her culture and found that it was resistant to erythromycin but susceptible to clindamycin. According to the guidelines, what antibiotic should I give her intrapartum for prophylaxis?
A: The choice of antibiotic for prophylaxis in this situation depends on whether the laboratory also tested for inducible clindamycin resistance. GBS resistant to erythromycin can also have inducible resistance to clindamycin; ordinary susceptibility testing won’t detect this. A separate test must be done for inducible resistance, in addition to susceptibility testing.
If the laboratory tested for inducible resistance to clindamycin and it was not found, then you should use clindamycin for intrapartum prophylaxis (Figure 8). If testing showed inducible resistance to clindamycin (positive result) then you must use vancomycin for intrapartum prophylaxis.
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